Super-soft, non-itchy, wonderfully warm, and a great moisture-wicker, Merino wool can’t be beat for base layer tops. When temperatures fall steeply, a good base layer is the starting point for keeping your body toasty (beneath additional layers, of course). If the day turns warm, peel down to your base layer and you’re ready to keep skiing, hiking, or riding your bike.

-REI Co-op’s Merino Midweight Half-Zip Base Layer Top for women has underarm gussets that provide a full range of motion, a zipper with a chin guard that allows ventilation adjustment, is fitted to hug a woman’s body, weighs less than 8 ounces, and is machine washable. Comes in five colors. Currently reduced from $89.50 to $53.69. www.rei.com

-Smartwool’s Men’s Merino 250 Base Layer Pattern Crew, the company’s warmest base layer, is a handsome crew with contrasting-color set-in sleeves. Flatlock seams help eliminate chafing, it’s super-comfy, and the crew is machine washable. Comes in black/light gray only. $105. www.smartwool.com

-Icebreaker’s Kids’ Compass Long Sleeve Half Zip, midweight and 100% merino, keeps children warm. It’s got a zip-neck collar, an interior storm flap, and flatlock seams to prevent chafing. Three colors (black, navy, wild rose). Currently reduced to $52.50 from $70. www.icebreaker.com

- Icebreaker products are carried by Sonoma Outfitters in Santa Rosa.

- REI products can be found at REI in Santa Rosa.

- Smartwool products are carried by Dick’s Sporting Goods (Santa Rosa and Petaluma); Fleet Feet Sports, REI, Sonoma Outfitters, and Birkenstock Village (Santa Rosa); and Silk Moon (Sebastopol).